Fuel tank or filler pipe for this tank

ABSTRACT

Fuel tank or filler pipe for this tank comprising a multilayer wall constituted at least of one layer based on a reinforced thermoplastic composition and of one inner layer, intended to be in contact with the fuel, based on a non-reinforced thermoplastic composition. Use of such a tank/pipe in a hybrid vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage entry under 35 U.S.C. §371 of International Application No. PCT/EP2010/057763 filed Jun. 3, 2010, which claims priority to French Application No. 09.02755 filed on Jun. 8, 2009, the whole content of this application being herein incorporated by reference for all purposes.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a fuel tank or a filler pipe for this tank, and also to their use as a tank/pipe in a hybrid-engine vehicle.

BACKGROUND OF THE INVENTION

Hybrid engine generally refers to the combination of a combustion engine and an electric motor.

There is a general operating principle for hybrid engines that consists in operating either the electric motor, or the combustion engine, or both at the same time, depending on the model.

One of the particular principles is as follows:

-   -   during stationary phases (when the vehicle is stationary), both         engines are shut down;     -   at start-up, it is the electric motor which sets the vehicle in         motion, up to higher speeds (25 or 30 km/h);     -   when higher speed are reached, the combustion engine takes over;     -   in the event of fast acceleration, both engines operate at the         same time, which makes it possible to have accelerations         equivalent to the engine of the same power, or even greater         accelerations;     -   in the decelerating and braking phase, kinetic energy is used to         recharge the batteries (it should be noted that this         functionality is not available in all the hybrid engines that         are currently commercially available).

It results from this principle that the combustion engine does not operate constantly and that consequently, the purge phases of the canister (activated carbon filter that prevents fuel vapors being released to the atmosphere) cannot be carried out normally since during these purge phases air, which is optionally preheated, is circulated through the canister in order to regenerate it (i.e., in order to desorb the fuel vapors that are adsorbed therein), this air then being admitted into the engine in order to be burnt therein. Moreover, hybrid vehicles were developed in order to reduce fuel consumption and emissions of exhaust gases, which makes the engine management for burning the fuel vapors coming from the canister more complex, or even impossible, without deteriorating the engine performance.

Therefore, the fuel tanks of these engines are generally pressurized (typically to a pressure of around 300-400 mbar) in order to limit loading of the canister, which is generally carried out by a functional element located after the ventilation valves, known as an FTIV (Fuel Tank Isolation Valve). This element comprises a safety valve (calibrated to the maximum working pressure of the tank) and an electric control in order to be able to bring the tank to atmospheric pressure before filling. As a result these tanks must have, compared to the fuel tanks of conventional combustion engines, an improved mechanical strength, in particular in the case of plastic tanks.

The solution currently on the market consists of a metal tank of important thickness, which considerably increases the weight of the tank and thus increases the fuel consumption and the exhaust gas emissions.

Other known solutions to the aforementioned pressure problem may consist of an increase of the wall thickness of plastic tanks and/or in the use of internal reinforcements (rods, partitions, etc.) connecting the two walls together, but these solutions generally adversely affect the weight, reduce the working volume of the tank and increase the cost of the tank. Another solution may consist in providing the tank with attachment studs (or kiss points i.e., local welds of the lower wall and of the upper wall), but this solution leads to a reduction of the working volume of the tank.

Another solution is that described in U.S. Pat. No. 5,020,687 which consists in attaching a reinforcing fabric to the outer wall of the tank, this attachment taking place by overmolding said fabric during the manufacture of the tank by extrusion-blow molding, the fabric being introduced into the mold prior to the introduction of the parison which, after blow molding, will give the tank.

However, this solution has several drawbacks:

-   -   the fabric in fact exerts only a local reinforcement, at the         location where it is attached;     -   in the long term, the diffusion of fuel vapors through the tank         wall may lead to problems of swelling, or even of loss of         adhesion of the fabric to the tank wall, hence reducing the         reinforcing effect;     -   by virtue of the technique used, there are limitations in terms         of fabric thickness and/or mold geometry;     -   and lastly: such a type of reinforcement is relatively         expensive.

SUMMARY OF THE INVENTION

One subject of the present invention is therefore a fuel tank or a filler pipe for this tank which has good long-term mechanical strength without suffering from the aforementioned drawbacks.

It is based on the idea of using a reinforced plastic composition, i.e., a plastic in which a reinforcement (in particular, a fibrous reinforcement) has been dispersed/mixed (for example: in the molten state of the plastic, using an extruder), which is known per se, but not using such a composition in the inner layer of a multilayer tank (i.e., the one which is in contact with the fuel), but only in the outer layer and/or in an intermediate layer, where appropriate. The applicant has in fact observed that when the inner layer of the tank comprises a reinforcement (in particular: when it comprises fibers), the impact strength of the tanks was greatly reduced, to the extent that they no longer pass the standards imposed by motor vehicle manufacturers. On the other hand, on condition that a non-reinforced inner layer is provided that has a sufficient thickness (the value of which depends on the composition of said layer, but which is generally at least 20%, or 30% or even 40% of relative thickness), such a reduction is no longer observed, and even better: a substantial improvement is even observed in certain cases.

The present invention therefore relates to a fuel tank or filler pipe for this tank comprising a multilayer wall constituted at least of one layer based on a reinforced thermoplastic composition and of one inner layer, intended to be in contact with the fuel, based on a non-reinforced thermoplastic composition.

The fuel for which the tank/pipe according to the invention is intended may be petrol, diesel, a biofuel, etc. and may have an alcohol content of 0 to 100%.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The expression “tank or pipe” is understood to mean any tank or pipe obtained by molding or by coextrusion of at least the two aforementioned layers.

A molding operation that can be used for the manufacture of a tank or pipe of finite length in accordance with the invention may be of any nature, as long as it includes the use of a mold that determines the shape of the tank or of the pipe. This molding operation may be carried out, for example, starting from a preform or directly by introducing the gelled thermoplastic into the mold.

The molding operation may also be coupled, in particular, to a blow-molding operation. It may also be followed by a subsequent assembly step, especially by welding. If the molding operation is carried out starting from a preform, this preform may be obtained, in particular, by coextrusion or coinjection.

Very good results have been obtained using molding by coextrusion-blow molding, molding by coinjection-welding or else molding by thermoforming. Preferably, the multilayer tank or pipe is produced by coextrusion-blow molding. In the latter case, it is possible to use a continuous extrusion technique or else an accumulating extrusion technique or a sequential extrusion technique, all techniques that are well known to those skilled in the art.

The term “thermoplastic” is understood to mean any thermoplastic polymer, including thermoplastic elastomers, and also blends thereof. The term “polymer” is understood to mean both homopolymers and copolymers (especially binary or ternary copolymers), for example random copolymers, linear block copolymers, other block copolymers and graft copolymers, etc.

The plastic of the inner layer and that of the reinforced layer may be (and preferably are) of the same nature. In the case of fuel tanks, this is generally a polyolefin. The term “polyolefin” is understood to mean any olefin homopolymer, any copolymer containing at least two different olefins and any copolymer comprising at least 50% by weight of units derived from olefins. Several polyolefins may also be used in the blend. More particularly, the blend may contain a certain proportion of recycled polyolefin in addition to the virgin polyolefin, or else a certain proportion of a blend of recycled resins originating (i) from the grinding of scrap obtained at various stages of the manufacture of the multilayer tank or pipe and/or (ii) from the recycling and treatment of end-of-life fuel tanks. The blend may also comprise a polyolefin of plant origin or from another renewable source (biomaterials).

Preferably, the polyolefin is a polyethylene. Very good results have been obtained with a high-density polyethylene (HDPE).

The plastic compositions may comprise customary additives such as one (or more) stabilizer(s), lubricant(s), pigment(s) and other “fillers” provided however that the additive(s) of the inner layer do not have a reinforcing effect and/or are present in an amount such that they do not have a significant effect on its mechanical properties.

The term “reinforced” is understood, within the context of the present invention, to mean comprising a (mixture of) reinforcement(s) in the dispersed state (i.e., in the form of “free” particles, mixed with the plastic, as opposed to woven or entangled particles (fibers) as in a woven fabric or a mat), in an amount such that it has a significant influence on the mechanical properties of the composition. At this stage a distinction should be made between (i) microscopic fillers/reinforcements for which a significant influence on the properties is obtained with high filling levels (typically greater than 10%) and (ii) nanofillers for which large variations in properties are obtained with only a few % of reinforcements.

Generally, these are fibrous reinforcements (carbon fibers, natural fibers, glass fibers, etc.), beads (for example glass beads, generally hollow beads) or platelets (talc, clays, montmorillonite, vermiculite, expanded graphite, graphene for example). They are preferably fibers. Powders (carbon black, chalk, talc, barium sulfate, etc.) are not generally considered to be reinforcements within the context of the invention except, of course, for those which could have a significant impact on the mechanical properties of the composition. Glass fibers give good results within the context of the invention, and, in particular, short and long glass fibers. For the short fibers, good results have been obtained by dispersing, in HDPE, fibers based on E-type glass (in particular provided with a sizing agent and/or a compatibilizer such as PE-g-MAH), having a diameter between 10 and 20 μm and an initial length between 2 and 8 mm.

According to one preferred variant, glass fibers are chosen as the reinforcement that are incorporated (preferably homogeneously, generally by mixing in an extruder in order to make masterbatch granules) in an amount of 10-50% (by weight versus the complete weight of the mixture), or even 20-40%, a content of around 30% generally giving good results, in particular in an intermediate layer and very particularly in a layer made from grindings as described above.

Indeed, the applicant has blow molded bottles respectively based on virgin HDPE (Lupolen® 4261AG, density of 0.945 g/cm³ and HLMI of 6 g/10 min (190° C./21.6 kg)) in a single-layer structure, and bottles based on this same HDPE but that comprise a layer of industrial regrinds of 6-layer tanks as defined above, between two layers of virgin PE of around 45% relative thickness (with respect to the total thickness of the wall) for the inner layer and 20% relative thickness for the outer layer. The applicant varied, over several tests, the content of glass fibers and observed respectively the properties that appear in the table that appears at the end of the present description.

In particular when it comprises at least one polyethylene-based layer, the tank according to the invention preferably also comprises a barrier layer and/or has preferably been subjected to a surface treatment (for example: to a fluorination or a sulfonation of its inner layer). It preferably comprises a barrier layer also made of a thermoplastic, which is generally either the inner, non-reinforced layer of the tank, or an intermediate layer between the inner layer and the reinforced layer.

The barrier resin that can be used within the context of this variant of the invention may be of any nature known to those skilled in the art as long as it is a polymer or copolymer that is compatible with the molding technique in question. It may also be a mixture of various barrier resins. Among the resins that can be used, mention is especially made of polyamides or copolyamides, or random ethylene/vinyl alcohol (EVOH) copolymers.

The term “polyamide” is understood to mean any homopolymer based on an amide unit, any copolymer comprising at least two different amide units and any copolymer comprising at least 50% by weight of units derived from an amide. It does not matter whether the amide units of this definition are obtained by the opening of the ring of a cyclic polyamide or by the polycondensation of a dicarboxylic acid with a diamine. Several polyamides may also be used as a blend. As examples of polyamides that can be used, mention may be made, in a non-limiting way, of: PA-6, PA-11, PA-12 and n-mXD6 (polyarylamide). PA-6 is generally preferred.

Advantageous results have been obtained in the case where the barrier resin is EVOH and in particular with an intermediate EVOH-based barrier layer between two layers of HDPE (generally by means of interposing two layers of PE-based adhesive at the two EVOH/HDPE interfaces). Advantageous results have also been obtained in the case where the barrier resin is a polyarylamide of n-mXD6 type constituting the inner layer of the structure.

The layer comprising the barrier resin may also comprise certain additives well known to those skilled in the art, which additives may or may not be polymeric, such as stabilizers, lubricants, etc.

Preferably, the layer comprising the barrier resin is essentially constituted of the barrier resin.

Generally (and this is incidentally the case with HDPE and EVOH or HDPE and the polyamide), the barrier resin and the thermoplastic resin of the other layers of the tank/pipe are not compatible. Therefore, generally at least one, or even two, layer(s) of adhesive is (are) provided between the barrier layer and the layer or the 2 other layers in contact with it. Alternatively or in addition, an adhesive that is compatible with the thermoplastic resin may be blended with this resin.

Preferably, the adhesive in question above comprises at least one functionalized polyolefin.

The expression “functionalized polyolefin” is understood to mean any polyolefin comprising, in addition to the units derived from olefins, functional monomer units. These functional monomer units may be incorporated into the polyolefin, either into the main chain, or into the side chains. They may also be incorporated directly into the backbone of said main and side chains, for example by copolymerization of one or more functional monomers with the olefin monomer(s) or else may result from the grafting of one or more functional monomers to said chains, after the manufacture of the polyolefin. In this case, the polyolefin/functionalized polyolefin blend may especially be produced in a single step, by reactive processing during the gelling step included in the process for manufacturing the tank or pipe.

In this variant of the invention, the functional monomer units are chosen from carboxylic acids, dicarboxylic acids and anhydrides corresponding to said dicarboxylic acids. Therefore, these units generally result from the copolymerization or grafting of at least one unsaturated monomer having these same functional groups. As examples of monomers that can be used, mention is especially made of acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride, fumaric anhydride and itaconic anhydride. Preferably, the functional monomer units result from the copolymerization or grafting of maleic anhydride.

The functionalized polyolefins thus described are well known to those skilled in the art and are commercially available.

In the case where the polyolefin is a polyethylene, it is particularly advantageous for the functionalized polyolefin to be a polyethylene grafted by means of maleic anhydride (PE-g-MAH), that is to say that the functional monomer units result from the grafting of maleic anhydride onto a polyethylene.

The multilayer tank or pipe according to the invention may advantageously comprise one or more additional layers comprising a recycled plastic, preferably as an intermediate layer (i.e., a layer located between two other layers).

The expression “recycled plastic” is understood to mean a plastic obtained by grinding the scraps obtained at various stages of the manufacture of a hollow body, in particular the tank/pipe according to the invention, or by grinding such objects at the end of their life time.

In this variant, the reinforcement may be incorporated into the recycled plastic layer(s). For doing this, it is enough to collect the particles from the aforementioned grinding and mix them with granules of a masterbatch comprising the filler and then feed this mixture into an extruder of the aforementioned coextrusion-blow molding installation. Alternatively, the regrinds may be used for the manufacture of a masterbatch having the desired reinforcement content. This variant is preferred as it enables the grindings to be reused as much as possible.

In one particularly advantageous embodiment of multilayer tank or pipe according to the invention, the latter comprises six layers: an inner layer (I) based on non-reinforced HDPE, a first layer of adhesive (A1) preferably based on PE-g-MAH, a layer comprising a barrier resin (B) (preferably, EVOH), a second layer of adhesive (A2) preferably based on PE-g-MAH, a layer based on recycled resin (R) comprising a reinforcement (preferably, glass fibers) and an outer layer (E) based on HDPE.

In this embodiment, it is advantageous for the relative distribution of the thicknesses to be as follows (for a total thickness of 1 to 10 mm, or even of 3 to 7 mm; generally in the vicinity of 6 mm): I: 30-50%, A1: 1-3%, B: 1-3%, A2: 1-3%, R: 30-60%, E: 5-20%. The following structure is advantageously used (to within a few %): 39/2/2/2/45/10 as % of the total thickness for each of the layers I/A1/B/A2/R/E respectively.

According to one particular embodiment, the layer E (in contact with the atmosphere) comprises a compound based on carbon black for the purpose of protecting against UV radiation.

Multilayer structures having two or three layers including one (inner) layer based on n-MXD6, one layer based on reinforced HDPE (optionally containing adhesive) and optionally one layer of adhesive (if the HDPE layer does not contain any) are also advantageous.

The present invention also relates to the use of a tank/pipe as described above as a fuel tank for a hybrid vehicle. This tank/pipe may also be used in a conventional vehicle, where the reinforcing effect obtained may be taken advantage of to avoid the use of the metal straps that are generally used to prevent the creep of the lower wall of the tank when the tank is fastened to the bottom of the vehicle body.

It should also be noted that the reinforcing effect obtained by the subject of the invention may be combined with the use of other known reinforcements such as straps, attachment studs, internal reinforcements (rods, partitions), overmolded fabrics, etc. mentioned above and any other type of both internal and external reinforcement.

The combination of the invention with these known techniques makes it possible to reduce the size and/or the amount of attachment studs, internal reinforcements (rods, partitions), overmolded fabrics, etc. Thus the weight of the final solution is minimized and the working volume of the tank is maximized.

Number of drops Yield Improvement Exam- GF without Young's stress in the ple GF content breakage modulus (MPa) deformation (1) (2) (wt %) (3) (MPa) (4) (5) (6)   1R none 0 10 — — —   2R all 15 1 — — — 3 R 15 10 — — — 4 R 5 10 — — —   5R none 0 10 511 20.4 1   6R none 0 6 601 19.9 1 7 R 10 10 731 22.7 1.1 8 R 20 9 1072 26.1 1.2 9 R 30 7 1285 28.9 2.2 10  E 30 9 1171 22.2 1.3 (1) Examples 1 to 4: 1-liter flasks; examples 5 to 10: 3-liter flasks; examples 1R and 5R: single-layer flasks and the other examples: multilayer flasks having inner (I)/intermediate (R)/outer (E) layers of relative thicknesses 45/40/15 approximately, the inner layer (I) being based on regrinds; the letter R indicates that it is a comparative example (not in accordance with the invention); (2) layer containing glass fibers; (3) flasks filled to 90% with a water/ethylene glycol (60/40) mixture, conditioned for 16 h at −40° C. and that were dropped from a height of 6 m; (4) and (5): according to the ISO 527/1 standard; (6) compared to a single-layer flask (tests 1R and 5R). Deformation of the flask at mid-height under a pressure of 500 mbar at ambient temperature measured by a GOM image acquisition system. 

1. A fuel tank or filler pipe for a fuel tank comprising a multilayer wall, said multilayer wall comprising at least one layer based on a reinforced thermoplastic composition and one inner layer, intended to be in contact with a fuel, based on a non-reinforced thermoplastic composition.
 2. The tank or pipe according to claim 1, being produced by coextrusion-blow molding.
 3. The tank or pipe according to claim 1, wherein the reinforced thermoplastic composition contains a fibrous reinforcement.
 4. The tank or pipe according to claim 3, wherein the fibrous reinforcement comprises glass fibers.
 5. The tank or pipe according to claim 4, wherein the glass fibers content of the reinforced layer is between 10 and 50%.
 6. The tank or pipe according to claim 1, wherein the multilayer wall of said tank or said pipe comprises a barrier layer between two high-density polyethylene (HDPE) layers, or is in direct contact with the inside of the tank or of the pipe.
 7. The tank or pipe according to claim 1, wherein the multilayer wall of said tank or said pipe comprises a layer based on recycled plastic.
 8. The tank or pipe according to claim 7, wherein the reinforcement is included in an intermediate layer based on recycled plastic.
 9. The tank or pipe according to claim 8, comprising six layers: an inner layer (I) based on non-reinforced high-density polyethylene (HDPE), a first layer of adhesive (A1), a layer comprising a barrier resin (B), a second layer of adhesive (A2), a layer based on recycled resin (R) comprising a reinforcement, and an outer layer (E) based on HDPE.
 10. A method comprising using the fuel tank or filler pipe for fuel tank according to claim 1 as a fuel tank/pipe for a hybrid vehicle. 